Chemical Characterization and Determination of the Anti-Oxidant Capacity of Two Brown Algae with Respect to Sampling Season and Morphological Structures Using Infrared Spectroscopy and Multivariate Analyses

Improvement of Alginate Extraction from Brown Seaweed (Laminaria digitata L.) and Valorization of Its Remaining Ethanolic Fraction

This study aimed to improve the conventional procedure of alginate isolation from the brown seaweed (Laminaria digitata L.) biomass and investigate the possibility of further valorization of the ethanolic fraction representing the byproduct after the degreasing and depigmentation of biomass. The acid treatment of biomass supported by ultrasound was modeled and optimized regarding the alginate yield using a response surface methodology based on the Box-Behnken design. A treatment time of 30 min, a liquid-to-solid ratio of 30 mL/g, and a treatment temperature of 47 °C were proposed as optimal conditions under which the alginate yield related to the mass of dry biomass was 30.9%. The use of ultrasonic radiation significantly reduced the time required for the acid treatment of biomass by about 4 to 24 times compared to other available conventional procedures. The isolated alginate had an M/G ratio of 1.08, which indicates a greater presence of M-blocks in its structure and the possibility of forming a soft and elastic hydrogel with its use. The chemical composition of the ethanolic fraction including total antioxidant content (293 mg gallic acid equivalent/g dry weight), total flavonoid content (14.9 mg rutin equivalent/g dry weight), contents of macroelements (the highest content of sodium, 106.59 mg/g dry weight), and microelement content (the highest content of boron, 198.84 mg/g dry weight) was determined, and the identification of bioactive compounds was carried out. The results of ultra high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry analysis confirmed the presence of 48 compounds, of which 41 compounds were identified as sugar alcohol, phenolic compounds, and lipids. According to the 2,2-diphenyl-1-picrylhydrazyl assay, the radical scavenging activity of the ethanolic fraction (the half-maximal inhibitory concentration of 42.84 ± 0.81 μg/mL) indicated its strong activity, which was almost the same as in the case of the positive control, synthetic antioxidant butylhydroxytoluene (the half-maximal inhibitory concentration of 36.61 ± 0.79 μg/mL). Gram-positive bacteria (Staphylococcus aureus, Enterococcus faecalis, and Bacillus cereus) were more sensitive to the ethanolic fraction compared to Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, and Shigella sonnei). The obtained results indicated the possibility of the further use of the ethanolic fraction as a fertilizer for plant growth in different species and antifouling agents, applicable in aquaculture.

Enhancing the Properties of Self-Healing Gelatin Alginate Hydrogels by Hofmeister Mediated Electrostatic Effect

The cross-linker-free hydrogels have gained attention due to their lack of need for chemically modified polymers, resulting in better biocompatibility. The hydrogel properties can be enhanced by altering physical forces such as electrostatics and H-bonds. Tuning the physical interactions between polymers, salts, and plasticisers can unlock new horizons in material properties. This article examines four different salts and mixtures to determine their impact on gelatin-alginate biomaterial design. Drug release, swelling, and rheological properties are represented using a 3-D plot, and optimum samples are identified. It is concluded that kosmotropes yield better release and swelling results than chaotropes. The physical interactions of these salts with polymers are explained using DLS and FTIR/ATR studies, and these findings are corroborated with release, swelling, and rheological analyses. Another aspect of the biomaterial, self-healing property, is also considered. A 3-D plot is prepared using release kinetics, gel strength, and recovery percentage (three important factors for self-healing hydrogels). Chaotropes are identified as better candidates for self-healing behaviour. However, when considering gel strength, release, and self-healing, kosmotropes are favourable. Hence, different salts can be selected based on the desired application for hydrogels. It is also concluded that electrostatic forces hinder the formation of H-bonds between polymer chains.

Dynamic cross-linking of an alginate-acrylamide tough hydrogel system: time-resolved in situ mapping of gel self-assembly

Hydrogels are a popular class of biomaterial that are used in a number of commercial applications (e.g.; contact lenses, drug delivery, and prophylactics). Alginate-based tough hydrogel systems, interpenetrated with acrylamide, reportedly form both ionic and covalent cross-links, giving rise to their remarkable mechanical properties. In this work, we explore the nature, onset and extent of such hybrid bonding interactions between the complementary networks in a model double-network alginate-acrylamide system, using a host of characterisation techniques (e.g.; FTIR, Raman, UV-vis, and fluorescence spectroscopies), in a time-resolved manner. Further, due to the similarity of bonding effects across many such complementary, interpenetrating hydrogel networks, the broad bonding interactions and mechanisms observed during gelation in this model system, are thought to be commonly replicated across alginate-based and broader double-network hydrogels, where both physical and chemical bonding effects are present. Analytical techniques followed real-time bond formation, environmental changes and re-organisational processes that occurred. Experiments broadly identified two phases of reaction; phase I where covalent interaction and physical entanglements predominate, and; phase II where ionic cross-linking effects are dominant. Contrary to past reports, ionic cross-linking occurred more favourably via mannuronate blocks of the alginate chain, initially. Evolution of such bonding interactions was also correlated with the developing tensile and compressive properties. These structure-property findings provide mechanistic insights and future synthetic intervention routes to manipulate the chemo-physico-mechanical properties of dynamically-forming tough hydrogel structures according to need (i.e.; durability, biocompatibility, adhesion, etc.), allowing expansion to a broader range of more physically and/or environmentally demanding biomaterials applications.